1. Field of the Invention
The invention relates to a headrest support structure that pivotally supports a headrest.
2. Description of Related Art
One known headrest support structure makes a headrest serve as a dynamic damper by pivotally elastically-supporting the headrest on a seat back. The support structure described in Japanese Utility Model Application Publication No. 61-149552 (JP 61-149552 U), for example, is one such headrest support structure.
FIG. 7 is a view of the structure of a headrest support structure described in JP 61-149552 U. This headrest support structure has a bracket 51 that is fixed to a seat back frame 50 that is a frame member of a seat back. The bracket 51 is formed by a metal plate member that is bent in a general sideways U-shape. Through-holes 52 and 53 are formed in an upper portion and a lower portion, respectively, of this bracket 51. Headrest supports 54 that are made of resin and support headrest stays are inserted into these through-holes 52 and 53. The through-hole 52 formed in the upper portion of the bracket 51 is a slotted hole that is long in a seat front-rear direction. A wire-like spring 55 that is made of metal extends across a portion that is toward the seat front.
With this kind of headrest support structure, the headrest supports 54 is allowed to pivot ever so slightly with respect to the bracket 51 while being elastically supported. Therefore, with a seat in which the headrest is supported by this kind of support structure, the headrest serves as a dynamic damper that reduces seat vibrations by resonance vibration of the headrest.
When the headrest is used as a dynamic damper, the damper property of the headrest needs to be appropriately set such that the resonance frequency of the headrest matches the frequency of reduced seat vibration. With the headrest support structure according to the related art, unless the fit of the headrest supports 54 in the through-holes 52 and 53 of the bracket 51 is sufficiently tight, the position of the pivot center of the headrest supports 54 with respect to the bracket 51, and thus the position of the pivot center of the headrest, will change, and as a result, the damper property of the headrest will end up changing. However, if the fit of these headrest supports 54 is tight, assembly of the headrest supports 54 into the brackets 51 may be difficult.
Also, even if the headrest is not used as a dynamic damper, when the headrest is pivotally supported on the seat back, a similar problem may occur. That is, if the position of the pivot center of the headrest ends up being offset due to assembly tolerance of the members, the headrest will be unable to pivot as intended. On the other hand, in order to inhibit the position of the pivot center of the headrest from being offset, the fit of the members needs to be tight, but if the fit is tight, assembly of the part may be difficult.